This invention relates to a blend of polymers which has the characteristics of a thermoplastic elastomer.
Thermoplastic blends of partially cured monoolefin copolymer rubber with a polyolefin plastic, which exhibit elastomeric properties, are known (U.S. Pat. Nos. 3,758,643; 3,806,558; and 3,862,106 to Fischer, the disclosure of which is hereby incorporated by reference, issued Sept. 11, 1973; Apr. 23, 1974; and Jan. 21, 1975 respectively). Generally, such materials have not included additional elastomeric materials, and hence their performance, as measured by certain physical properties, has been limited.
The present invention is based on the discovery that the addition of a conjugated diene rubber to a blend of monoolefin copolymer rubber and polyolefin resin, followed by partial cure, unexpectedly results in a thermoplastic elastomeric composition which exhibits the highly desirable properties of low compression set and high tensile strength at elevated temperatures.